Rails 3.1 asset pipeline: how to deal with requests to expired assets?

Once you've set up an application with the asset pipeline, it might generate an image for you with a URL like this (signature truncated):

http://mysite.com/assets/logo-1b2b3c.png

Then, when you change the asset or update the global asset version, you end up with something like this:

http://mysite.com/assets/logo-2b3c1a.png

Now, some people will still be sending requests to the old asset. Under what I understand to be the default Rails 3.1 deploy, these would just 404. That doesn't seem very friendly. It would be nicer to either 301 to 开发者_StackOverflow中文版the new asset or just deliver the new asset straight up.

Is there some built-in way to do this, or do I have to implement my own asset missing feature?

I implemented it myself:

Myapp::Application.routes.draw do
  match 'assets/:id.:format' => 'assets#show'
end

class AssetsController < ApplicationController
  def show
    asset_without_digest = "#{params[:id].gsub /-[0-9a-f]{32}$/, ''}.#{params[:format]}"
    new_path = ActionView::Base.new.image_path(asset_without_digest)
    if url_for(params).include? new_path
      head 404
    else
      redirect_to new_path, :status => 301
    end
  end
end